Camera tube with faceplate heating means

ABSTRACT

A camera tube is disclosed which is useful for low temperature applications. The faceplate of the camera tube is heated by a transparent conductive coating which provides a current path between two electrodes spaced apart from one another and located at the peripheries of the faceplate. Uniform heating of the faceplate is thereby achieved. The photosensitive coatings on or adjacent the faceplate are thereby heated to provide an operating temperature independent of the low temperature environment.

United States Patent Simpson [4 1 Aug. 1, 1972 [54] CAMERA TUBE WITH FACEPLATE 3,360,671 12/1967 Salgo et a1 ..313/65 A HEATING MEANS FOREIGN PATENTS OR APPLICATIONS [72] Inventor: Kenneth R. Simpson, North Syracuse, 213,459 11/1956 Australia ..313/65 R Assign: General Company Primary Examiner-Robert Segal [22] Filed: Feb. 10, 1971 Attorney-Nathan J. Cornfeld, John P. Taylor, Frank L. Neuhauser, Oscar B. Waddell and Joseph B. For [21] App1.No.: 114,259 man [52] US. Cl ..313/65 R, 313/37, 313/44, ABSTRACT 219/543 A camera tube is disclosed which is useful for low [5 Illt- Cl. temperature applications. The faceplate of t camera [58] Field of Search ..219/543, 313/65 R, 37, 94 tube is heated by a transparent conductive coating which provides a current path between two electrodes [56] References (med spaced apart from one another and located at the UNITED STATES PATENTS peripheries of the faceplate. Uniform heating of the faceplate is thereby achieved. The photosensitive 1,133,435 3/ 1915 Fessenden ..313/94 X coatings on or adjacent the faceplate are thereby 2,730,598 1/1956 Lytle ..219/543 heated to provide an operating temperature indepen 2,882,377 4/1959 Rinehart ..219/543 X dent of the low temperature environment 3,060,388 10/1962 Selby et a1. ..313/94 3,063,881 11/1962 Harwig ..219/543 X 3 Claim, 3 Drawing Figures PATENTEDMJI; 1 i912 FIG.|.

FIG.2.

INVENTORZ KENNETH R. SIMPSON, BY 4% Hi8 TTORNEY.

CAMERA TUBE WITH FACEPLATE HEATING MEANS BACKGROUND OF THE INVENTION Camera tubes such as image orthicons or vidicons contain photosensitive members on or adjacent the faceplate of the camera tube. These photosensitive members are also sensitive to large changes in temperature. For example, when a vidicon is operated at very low temperatures, such as, for example, encountered in space, excessive changes in dark current, light sensitivity, and lag are noted.

For this reason, the prior art has attempted to heat the faceplate of the camera tube to provide a minimum operating temperature which is above the temperature of the environment. It has been proposed, for example, to place a heater coil around the camera tube adjacent the faceplate either on the periphery of the end surface of the faceplate itself, or on the end of the cylindrical portion of the tube adjacent the faceplate. In either case the heat must be conducted not only through the thickness of the glass but laterally across the surface of the glass to heat the center portions of the faceplate. Since the glass faceplate is chosen for its optical and mechanical properties and is usually a poor heat conductor; the result is a very inefficient and non-uniform heating of the faceplate.

SUMMARY OF THE INVENTION It is therefore an object of the invention to provide an improved camera tube for low temperature'applica tions wherein the'faceplate is uniformly heated by an efficient heater.

This and other objects of the invention will be apparent from a reading of the description and the accompanying drawings.

In accordance with the invention, an improved camera tube is provided comprising an evacuated en velope having a transparent faceplate adjacent one end and an electron beam generating means within the envelope and spaced apart from the faceplate. Photosensitive means are located adjacent the inner surface of the faceplate and electron optic means guide the electron beam to the photosensitive means. The outer surface of the faceplate is covered by a substantially transparent conductive coating. A plurality of electrodes are attached to the peripheries of the faceplate in ohmic contact with the conductive coating. A source of electrical power is connected to the electrodes to provide a current path through the conductive coating across the faceplate to provide a uniform heating of the faceplate.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-section of a camera tube of the invention.

FIG. 2 is a front elevational view front surface of the camera tube of FIG. 1.

FIG. 3 is a variation of the structure shown in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1 a camera tube is generally indicated at 2. Camera tube 2 comprises an evacuated envelope which is conventionally formed of glass and may be generally cylindrically shaped and having a front window 6 formed on one end of the cylinder. Within envelope 4, electron beam generating means 10 are located at a point spaced apart from window 6. Photosensitive means 20 comprise (in the illustrated embodiment) a photoconductive layer such as, for example, antimony trisulphide. Electron optic means 30 are provided to direct the beam to selected portions of photoconductive surface 20. Electron optic means 30 may comprise deflection plates to deflect the beam in both the x and y planes. Electron optic means 30 may also comprise focusing means (not shown) to focus the electron beam upon photosensitive layer 20. Signal means 40 are connected to a thin, optically transparent, conducting layer 22 sandwiched in between photosensitive layer 20 and glass window 6 to sense the photoconductivity of the layer 20 at any given point when the beam is focused thereon as is well known in the art.

In accordance with the invention, a substantially transparent conductive layer 8 is located on the front surface 6a of window 6. Conductive layer 8 comprises a very thin layer of a conductive material such as tin oxide or gold which is placed directly on the surface of 6a of window 6 by, for example, a vacuum deposition of the material onto surface 6a. The thickness of the material is determined by its light transparency and its conductivity per square. Preferably, the conducting layer should be less than 1 micron in thickness (to provide sufficient light transmission) yet be sufficiently thick to provide a resistivity of about ohms per square.

A pair of conductors l2 and 14 are placed on window 6 at the periphery of coating 8 and in ohmic con tact therewith. As more clearly seen in FIG. 2, conductors 12 and 14 provide the opposite electrodes which, when connected to an exterior source of power 16, provide the source of power to be transmitted across the surface of or through conductive layer 8. Conductors 12 and 14 may be applied by evaporating, for example, aluminum through a mask or by painting a conductor such as silver on window 6.

In a specific example a tin oxide layer of about 0.2-0.3 microns was deposited on the surface of a glass faceplate of approximately 1 inch diameter. Electrodes l2 and 14 as illustrated in FIG. 2 were deposited in parallel arrangement on opposing peripheral edges of the front surface of the faceplate by painting a conductive silver paint on the faceplate. The distance between the electrodes was approximately 0.75 inch and the resistance was 144.0. The electrodes were attached to an 18.8 volt DC source of power. A current of approximately 0.13 amperes was measured providing a power of approximately 2.5 watts. By measuring the temperature at various points on the coated faceplate it was determined that the temperature variation was less than 5 percent of the average temperature of the faceplate. The faceplate was assembled into a vidicon camera tube and the temperature of the faceplate member (with the camera tube in a low temperature environment of approximately 50 C.) was measured and found to be 15 C.

Referring now to FIG. 3 an alternate embodiment is illustrated wherein the electrodes 12' and 14' instead of resembling chords are shaped as arcs having inner, facing, edges of similar curvature to the outer curvature of the faceplate. Other configuration of electrodes 12 and 14 are, of course, also conceivable and are to be considered to be within the scope of the invention. The particular choice of the electrode shape may depend upon various factors such as the design of the overall tube as well as the case into which the tube will be placed as well as considerations of the equipment to be used to deposit the electrode on the surface.

While a vidicon has been illustrated having a photoconductive surface or layer coated on the faceplate of the tube, it will be obvious to those skilled in the art that a camera having a photocathode layer can also be used and is to be deemed to be within the scope of the invention. In either case the invention provides an; efficient heating of the faceplate having low power requirements as well as providing a more uniform heating of the entire surface of the faceplate. Thus, the photosensitive material adjacent the faceplate, whether the material be photoconductive or photoemissive, is uniformly heated to a constant temperature to provide more predictable photosensitive characteristics which are substantially independent of the low temperature environments in which the tube may be used. While particular materials have been described for use as the conductive transparent material to be coated on the front surface, it will be obvious to those skilled in the art that any material which provides the proper light transparency and resistivity may be used in place of the tin oxide or gold layer. Other modifications will also be apparent to those skilled in the art and should be deemed to be within the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. A camera tube capable of use in low temperature environments comprising an evacuated envelope containing electron beam generating means; a transparent window spaced apart from said beam generating means photosensitive means on the inner surface of the window; and means for uniformly heating said window comprising a. a pair of spaced-apart conductors on the outer surface of said window,

b. a substantially transparent, conductive coating of less than 1 micron in thickness interconnecting said conductors and having a resistivity of about 70 ohms per square,

0. a source of electric current connected to said conductors to provide a current flow across said conductive coating to heat said window to a temperature of at least 15 C. in an environment as low as 50 C.

2. The camera tube of claim 1 wherein said conduc tive coating has a thickness of about 0.2-0.3 microns.

3. The camera tube of claim 1 wherein said conductive coating comprises tin oxide. 

1. A camera tube capable of use in low temperature environments comprising an evacuated envelope containing electron beam generating means; a transparent window spaced apart from said beam generating means photosensitive means on the inner surface of the window; and means for uniformly heating said window comprising a. a pair of spaced-apart conductors on the outer surface of said window, b. a substantially transparent, conductive coating of less than 1 micron in thickness interconnecting said conductors and having a resistivity of about 70 ohms per square, c. a source of electric current connected to said conductors to provide a current flow across said conductive coating to heat said window to a temperature of at least 15* C. in an environment as low as -50* C.
 2. The camera tube of claim 1 wherein said conductive coating has a thickness of about 0.2- 0.3 microns.
 3. The camera tube of claim 1 wherein said conductive coating comprises tin oxide. 